Simon Kim Gye-wan, also called `Baek-sim`, was born to a common class family in Seoul. He ran a drugstore in town. In 1791 he obtained Catholic books from Thomas Choe Pil-gong. While reading these books, he was attracted by the reasonable doctrine of Catholicism. He decided to believe in it and was baptized by John Choe Chang-hyeon. He was arrested during the Sinhae Persecution that broke out that year. Because his faith was very weak he denied his religion and was released.

Returning home, Simon Kim sincerely repented his mistake, renewed his faith in God and resolved to live even more fervently. In late 1794, when Father James Zhou Wen-mo came to Korea and lived in hiding, Simon Kim tried to provide him with a place of safety in co-operation with fellow Catholics. He formed a community of the faithful to study Catholic teaching and visited Father James Zhou to receive the Sacraments. He helped with church activities and became Father James Zhou‘s altar server.

When Thomas Choe was arrested around December 1800, he hid in Juliana Kim Yeon-i`s house. A full-scale persecution broke out in early spring of 1801. His name was revealed during interrogations of the faithful, and the police searched for him in every direction. He no longer took refuge in Kim Yeon-i`s house but went from one place to another.

Meanwhile, his old father was arrested by the police. Simon too was arrested by the police while he was traveling from place to place looking for information about his family. Severe interrogation and torture were begun on Simon Kim. However, he stood firm and professed his faith in God with great heroism. He said to the interrogator, "It is impossible to give up my religion which I have believed in, for many years. I have a father who is very old, and I would like to be able to care for him but I think that filial piety to God is more important than that to my earthly father, even though it will be difficult to care for him."

As the interrogation continued, Simon Kim`s faith in God grew stronger and stronger. The judge and executioners were all puzzled to hear him stating that "I am strongly resolved more than ever to live out the teachings of my faith."

He was transferred to the Justice Ministry, where he was interrogated and tortured one more time, after which he was sentenced to death. He was beheaded outside the Small West Gate or Saenamteo in Seoul with his fellow believers on January 29, 1802 (December 26, 1801 by the Lunar calendar) and died a martyr.
Before he was sentenced to death, he made the following statement:

"I am an ignorant man. But I am deeply imbued with the Catholic religion and have believed in it for many years. Though I am suffering under cruel torture now, I have not the slightest intention of changing my mind. I truly believe in what my religion teaches me."